Sensor for accurate measurement of levels in irregularly shaped tanks

Abstract

A sensor for measuring the filling level of a fluid in a vessel, in particular fuel tank is disclosed. The sensor has an electrode group which extends vertically over the fillable vessel height, and dips into the fluid and which forms electrical capacitors whose capacitances change in a measurable fashion when there are changes in the filling level. The capacitances are determined by a connected evaluation circuit and are represented as a signal which describes the filling level. There is at least one measuring electrode which extends over the entire fillable vessel height. A plurality of reference elements are arranged at different reference heights within the fillable vessel height. Optionally, a plurality of measuring electrodes are arranged in such a way that each measuring electrode has a significant change in width at a reference height assigned to it, and wherein the entire fillable vessel height is passed over by the measuring electrodes. An advantageous method for measuring the filling level is also disclosed.

What is claimed is:  
     
       1. A sensor for measuring the filling level of a fluid in a non-uniform vessel, which comprises: 
       an electrode group which extends vertically over the fillable vessel height which dips into the fluid and which forms electrical capacitors whose capacitances change in a measurable fashion when there are changes in the filling level, the capacitances being determined by a connected evaluation circuit and being represented as a signal which describes the filling level;  
       wherein there is at least one measuring electrode which extends over the entire fillable vessel height; and  
       wherein a plurality of reference elements are arranged at different reference heights within the fillable vessel height and the distance separating each reference element is determined such that the volume between each reference element is equivalent.  
     
     
       2. The sensor of claim  1  wherein there are a plurality of measuring electrodes (E S1  to E S4 ) which are arranged in such a way that each measuring electrode (E S1 , to E S4 ) has a significant change in width at a reference height (H 1 , H 2 , H 3 ) assigned to it, and wherein the entire fillable vessel height (H ges ) is passed over by the measuring electrodes (E S1 , to E S4 ). 
     
     
       3. The sensor of claim  1 , wherein there is an opposing electrode (E 0 ) which forms electrical capacitors with all the measuring electrodes (E S ; E S1 , to E S4 ). 
     
     
       4. The sensor as claimed in claim  3 , wherein the reference elements (ER1 to E R5 ) are reference electrodes, and the one opposing electrode (E 0 ) also forms electrical capacitors with all the reference electrodes. 
     
     
       5. The sensor as claimed in claim  1 , wherein the reference elements (E R1  to E R5 ) are thermistors. 
     
     
       6. The sensor as claimed in claim  1 , wherein the distances between the reference heights (H 1 , H 2 , H 3 ) at small filling levels are smaller than at large filling levels. 
     
     
       7. The sensor as claimed in claim  1 , wherein the reference heights (H 1 , H 2 , H 3 ) are selected such that even when the vessel ( 1 ) is irregularly shaped, a regular division of the filling volume by the reference heights (H 1 , H 2 , H 3 ) is produced. 
     
     
       8. The sensor as claimed in claim  2 , wherein the electrode group is arranged on a bent carrier ( 40 ,  40 ′,  40 ″). 
     
     
       9. The sensor as claimed in claim  2 , wherein the evaluation circuit ( 42 ,  42 ′,  42 ″) is arranged on the same carrier ( 40 ,  40 ′,  40 ″) as the electrode group. 
     
     
       10. The sensor as claimed in claim  2 , wherein the carrier ( 40 ,  40 ′,  40 ″) for the electrode group is composed of enameled sheet steel. 
     
     
       11. The sensor as claimed in claim  2 , wherein the electrode group is implemented on its carrier ( 40 ,  401 ,  4011 ) as a printed circuit. 
     
     
       12. A method for measuring the filling level in a non-uniform vessel, using a filling level sensor having an electrode group which extends vertically over the fillable vessel height which dips into the fluid and which forms electrical capacitors whose capacitances change in a measurable fashion when there are changes in the filling level, the capacitances being determined by a connected evaluation circuit and being represented as a signal which describes the filling level; 
       wherein there is at least one measuring electrode which extends over the entire fillable vessel height; and  
       wherein a plurality of reference elements are arranged at different reference heights within the fillable vessel height such that the distance separating each of the reference elements results in an equivalent volume between the reference elements and wherein the filling level display is corrected with the discontinuities in the electrical behavior of the sensor which results owing to the arrangement of the measuring electrodes and the reference elements when the filling level changes beyond a reference height and wherein each of the reference elements have a shape proportional to the volume represented at the different reference heights.  
     
     
       13. The method as claimed in claim  12 , wherein the measurement signal of the filling level sensor ( 2 ) is corrected with a signal relating to the removal of fluid ( 51 ). 
     
     
       14. The method as claimed in claim  13 , wherein the total value of the removal of fluid ( 51 ) which is converted into a height value is subtracted from the last measured value of the filling level (H), at least between two reference heights (H 1 , H 2 , H 3 ), and the current measured value is corrected with the result.